546 LOUISE SMITH 



similar to those which Mile. Smirnova ('14) found in the his- 

 tology of metamorphosing frog muscle. For the order of de- 

 velopment of the various muscles from the larval condition to 

 that of the adult and for their appearance in sections I would 

 refer to the same table and plates as in the case of the skeleton. 

 The general method of muscle metamorphosis is typified in 

 the transformation of the thoracicohyoideus of the larva into 

 the abdominohyoideus and sternohyoideus of the adult. The 

 first indication of any change in the thoracicohyoideus appears 

 in stage I, when a proliferation and anterior growth of fibers 

 from that muscle brings the origin on to the dorsal surface of 

 the first basibranchial, considerably anterior to its articulation 

 with the plate (fig. 30). These new fibers, which are very small 

 and so quite easily distinguishable from the old, make up the 

 anlage of the abdominohyoideus muscle. Stage II shows the 

 origin of what is now^ quite unmistakably the abdominohyoideus 

 well forward in the connective tissue of the tongue, and the 

 beginning of the breaking down of the median portion of the 

 thoracicohyoideus. In this degenerative process I find, as Mile. 

 Smirnova did, that the muscle fibers first appear very large and 

 devoid of their cross-striations and then are interspersed with 

 muscle phagocytes which eventually dispose of them. As to 

 the nature of the phagocytes, however, my opinion differs from 

 hers, though I have insufficient data to prove my point con- 

 clusively. She states that they are formed by the muscle cells 

 themselves and are not leucocytes, but a careful comparison of 

 them with preparations of fresh human blood show^s such a 

 striking similarity to leucocytes of the polynuclear type that I 

 fail to see how they can be anything else. At this stage, also, 

 the differentiation of the ventral slip of the thoracicohyoideus 

 into the sternohyoideus begins by the degeneration of the more 

 dorsal fibers of the slip and ventral ones of the muscle proper 

 (fig. 36). The degeneration of the old and formation of the 

 new fibers continue anteroposteriorly, so that by stage III the 

 abdomino hyoideus is quite adult in position anteriorly, but 

 more posteriorly the whole position of the thoracicohyoideus is 

 filled in with degenerating fibers of that muscle, muscle phago- 



